1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member having a surface layer made up of hydrogenated amorphous silicon carbide and an electrophotographic apparatus having such an electrophotographic photosensitive member. The hydrogenated amorphous silicon carbide is hereinafter also expressed as “a-SiC”. The surface layer made up of the hydrogenated amorphous silicon carbide is hereinafter also expressed as “a-SiC surface layer”.
2. Description of the Related Art
Among various kinds of electrophotographic photosensitive members, an amorphous silicon electrophotographic photosensitive member is widely known which has a substrate such as a metal and formed thereon a photoconductive layer (photosensitive layer) made up of an amorphous material. The amorphous silicon electrophotographic photosensitive member is hereinafter also expressed as “a-Si photosensitive member”.
As an example of the make-up of such an a-Si photosensitive member, a make-up is available in which the photoconductive layer is formed on the substrate and the a-SiC surface layer is formed on the photoconductive layer. Since the a-SiC surface layer has an excellent wear resistance, it has chiefly been used in electrophotographic apparatus having a high process speed.
However, in any conventional a-SiC surface layer, it has come about in some cases that, when used in an environment having a high absolute humidity, blurred characters or letters are formed, or characters or letters are not printed to cause blank areas in images (hereinafter such a phenomenon is also expressed as “high-humidity image flow (or image deletion due to high-humidity)”).
The high-humidity image flow refers to a phenomenon of faulty images that, where images are reproduced using an electrophotographic apparatus placed in the environment having a high absolute humidity and images are again reproduced after a while, blurred characters or letters are formed, or characters or letters are not printed to cause blank areas in the images reproduced again.
The high-humidity image flow is considered to occur because the electrophotographic photosensitive member comes to have a low surface resistance upon adsorption of water on its surface to cause any electric charges thereon to flow transversely. Hence, it more tends to occur where the environment in which the electrophotographic apparatus is placed has a high absolute humidity or where a photosensitive member heater provided in the vicinity of the a-Si photosensitive member is not on use.
As a technique for keeping the high-humidity image flow from occurring, Japanese Patent No. 3124841 discloses a technique in which atom densities of various atoms making up the surface layer are set smaller than specific value and the a-SiC surface layer is formed to have a relatively coarse film structure so as to make the surface layer easily abradable in a cleaning process. Making the a-SiC surface layer easily abradable makes any charge products or water having come adsorbed on the surface removable with ease together with an oxide layer formed on the surface of the a-SiC surface layer, and hence this enables the high-humidity image flow to be kept from occurring.
In recent years, in the market, electrophotographic apparatus have made progress in high-speed and color image formation, and their process has changed into an electrophotographic process that makes the electrophotographic photosensitive member surface more tend to wear. Meanwhile, in the market, accompanied by such high-speed and color image formation, there is also a demand for an electrophotographic apparatus that enables stable reproduction of images having a high image quality. For such a commercial demand, it has come necessary to provide an electrophotographic photosensitive member improved in keeping the high-humidity image flow from occurring, while maintaining a good wear resistance.
In this regard, the employment of the technique disclosed in Japanese Patent No. 3124841 requires making the surface of the electrophotographic photosensitive member abrade at a certain speed, and hence tends to damage its durability especially in a high-speed electrophotographic process.
Stated specifically, in the technique disclosed in Japanese Patent No. 3124841, in order to remove the oxide layer formed on the surface of the electrophotographic photosensitive member or any charge products, water or the like having come adsorbed on the oxide layer (i.e., adsorbed matter), it has been necessary for the surface of the electrophotographic photosensitive member to be provided with a certain readiness to wear.
In addition, it has also come about in some cases that such a surface layer tending to wear comes to have pressure scars (or scratches) to make the lifetime of the electrophotographic photosensitive member limitative. The pressure scars refer to a phenomenon that a mechanical stress is applied to the electrophotographic photosensitive member surface to cause scratch-like image defects such as black line or white line on images. Such pressure scars tend to be conspicuous especially when halftone images are reproduced in a highly precise electrophotographic process, and are the cause of lowering image quality and also making the electrophotographic photosensitive member have a short lifetime.
That is, in conventional electrophotographic photosensitive members and electrophotographic apparatus, it has been difficult for them to be improved in keeping the high-humidity image flow from occurring, while maintaining a good wear resistance.